1. Field of the Invention
This invention relates to a power tool switchable among driving modes different in driving state of a tool bit.
2. Description of the Related Art
Japanese non-examined laid-open Patent Publication No. 2006-957 discloses a hammer drill which is capable of switching a driving mode of a tool bit in the form of a hammer bit between a hammer drill mode in which the hammer bit is caused to perform linear movement in its axial direction and rotation around its axis and a hammer mode in which the hammer bit is caused to perform linear movement in its axial direction. The known hammer drill has an operating mechanism that converts the rotating output of the motor into linear motion and then causes the hammer bit to linearly move via a striker, and a power transmitting mechanism that transmits the rotating output of the motor at reduced speed and causes the hammer bit to rotate. The power transmitting mechanism is provided with a mechanical claw clutch for switching the driving mode of the hammer bit. In order to switch the driving mode of the hammer bit between hammer drill mode and hammer mode, a mode switching member is operated to switch the claw clutch between a power transmission state and a power transmission interrupted state.
In the known claw clutch, when the driving mode of the hammer bit is switched from hammer mode to hammer drill mode by operating the mode switching member, driving-side clutch teeth and driven-side clutch teeth are engaged with each other, so that the clutch is shifted to the power transmission state.
Therefore, when the mode switching member is not switched to a normal hammer drill mode position and selection of the driving mode of the hammer bit is in a halfway state, the clutch teeth are also in halfway engagement. Driving of the hammer drill in such a halfway clutch engagement may cause acceleration of wear and decrease of durability.